Decomposition of the Seismic Source Using Numerical Simulations and Observations of Nuclear Explosions
Technical Report,01 May 2014,30 Apr 2017
Leidos San Diego United States
Pagination or Media Count:
We investigate the effects of explosion depth, tectonic stresses and topography on seismic waves from underground nuclear explosions. We perform three-dimensional calculations for an explosion inside and under a mountain, and then perform four three-dimensional calculations of an explosion at several depths in the topography of the North Korean test site. We also perform a large number of two-dimensional axisymmetric calculations of explosions at depths from 150 to 1000 meters in four earth structures, with compressive and tensile tectonic stresses and with no tectonic stresses. We find that P-waves are not strongly affected by any of these effects because the initial down going P-wave is unaffected by interaction with the free surface. Surface waves, however, are strongly affected by all of these effects. There is an optimal depth where surface waves are maximized at the base of a mountain and at or slightly below normal containment depth. At deeper depths, increasing overburden pressure reduces the surface waves. At shallower depths, interaction with the free surface reduces the surface waves. For explosions inside a mountain, displacement of the sides of the mountain reduces surface waves. Compressive prestress reduces surface wave substantially, while tensile prestress increases surface waves. The North Korean explosions appear to be at an optimal depth, in a region of extension, and beneath a mountain, all of which increase surface wave amplitudes. Measurements of Ms from Degelen and Shagan River explosions as small as 1.5 kilotons are consistent with the global average Msyield curve, while the North Korean explosions are high by about 0.6 magnitude units.
- Nuclear Explosions and Devices (Non-Military)